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“Terminator” fish worries scientists

Aug. 14, 2014
Courtesy of Oregon State University 
and World Science staff

A fish that’s in­vad­ing the At­lantic Ocean hunts more like the “ter­mi­na­tor” of mov­ie fame than like an or­di­nary pred­a­tor, wor­ried sci­en­tists say.

The red li­on­fish can hunt spe­cies to ex­tinc­tion lo­cal­ly, ac­cord­ing to re­searcher­s—un­like more com­mon pred­a­tors, which find it eas­i­er to leave prey alone and move on af­ter prey popula­t­ions have been re­duced.

Lionfish (scientific names Pterois volitans, Pterois miles), venomous fishes native to the Indo-Pacific and Red Sea.  (Cour­tesy NOAA)


Find­ings de­scribed as “alarm­ing” about the red li­on­fish, which came from the Pa­cif­ic Ocean, were pre­sented Aug. 14 at the an­nu­al meet­ing of the Ec­o­log­i­cal So­ci­e­ty of Amer­i­ca in Sac­ra­men­to. 

Sci­en­tists say the fish’s At­lan­tic in­va­sion, be­lieved to have be­gun in the 1980s, now co­vers an ar­ea larg­er than the whole Un­ited States, dec­i­mat­ing na­tive fish in parts of the Car­ib­be­an and else­where. The poi­son­ous lion­fish spines can in­jure peo­ple as well.

Most na­tive pred­a­tory fish are at­tracted to prey when their num­bers are high­—that’s when suc­cess­ful at­tacks are easy, ac­cord­ing to pre­vi­ous re­search by fish ecol­o­gist Mi­chael Web­ster. As the prey popula­t­ion falls, the na­tive pred­a­tors of­ten move on to ar­e­as where, lit­er­al­ly, the fish­ing is bet­ter. This pro­cess tends to sta­bi­lize prey popula­t­ions: they shrink when they get too large and grow when they get too small.

The new re­search found that li­on­fish, by com­par­i­son, seem to stay in one ar­ea even as the num­bers of prey drop, and in some cases can eat a popula­t­ion to lo­cal ex­tinc­tion. They have un­ique char­ac­ter­is­tics that make this pos­si­ble, and like the ter­mi­na­tor, they just will not stop.

They “seem to be the ul­ti­mate in­vader,” said Kurt In­ge­man, a doc­tor­al can­di­date in at Or­e­gon State Uni­vers­ity who pre­sented the find­ings, build­ing on pre­vi­ous work by his ad­vi­sor Mark Hixon and fel­low grad­u­ate stu­dents. “Al­most eve­ry new thing we learn about them is some char­ac­ter­is­tic that makes them a more for­mi­da­ble pred­a­tor. And it’s now clear they will hunt suc­cess­fully even when only a few fish are pre­s­ent. This be­hav­ior is un­usu­al and alarm­ing.”

In­ge­man con­ducted the re­search on rep­li­cat­ed nat­u­ral reefs in the Ba­ha­mas, meas­ur­ing the mor­tal­ity rates of a com­mon li­on­fish prey, the fairy basslet—a pop­u­lar aquar­i­um fish. A range of sce­nar­i­os was set up for ex­amina­t­ion: reefs with the in­va­sive li­on­fish, reefs with na­tive pred­a­tors alone, and var­i­ous popula­t­ion lev­els of fairy basslet. In­ge­man found that when prey fish were sparse, the mor­tal­ity with li­on­fish pre­s­ent was four times high­er than that caused by na­tive pred­a­tors alone.

“Reef fish usu­ally hide in rocks and crevices for pro­tec­tion, and with high popula­t­ions, there is a scram­ble for shel­ter,” In­ge­man said. “Na­tive pred­a­tors take ad­van­tage of this situa­t­ion by mostly eat­ing when and where prey are abun­dan­t.” In oth­er words, the pred­a­tors have an eas­i­er time when there’s simply not enough shel­ter to hide their prey.

Li­on­fish, how­ev­er, have such ad­van­tages as an in­va­sive spe­cies that they ap­par­ently feel no need to move on for bet­ter or eas­i­er hunt­ing, In­ge­man said. Oth­er fish may not rec­og­nize them as a pred­a­tor. Li­on­fish are al­so very ef­fi­cient hunters, are well de­fended them­selves by poi­son­ous spines, can thrive in deep wa­ters, tol­er­ate a wide range of con­di­tions, re­pro­duce quickly most of the year and aren’t picky eaters. Hixon and fel­low grad­u­ate stu­dents have found that li­on­fish can wipe out over 90 per­cent of more of the na­tive fish in some hard-hit ar­e­as.

Ev­o­lu­tion­ary pres­sures may eventually al­low na­tive fish to adapt and de­fend them­selves, In­ge­man said, but when and how is un­clear. “We know that fish can learn and change their be­hav­ior, some­times over just a few genera­t­ions. But we don’t have any stud­ies yet to dem­on­strate this is tak­ing place with na­tive fish popula­t­ions in the At­lantic.”


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A fish that’s invading the Atlantic Ocean hunts more like the “terminator” of movie fame than like an ordinary predator, worried scientists say. The red lionfish can hunt species to extinction locally, according to researchers—unlike more common predators, which find it easier to leave prey alone and move on after prey populations have been reduced. Findings described as “alarming” about the red lionfish, which came from the Pacific Ocean, were presented Aug. 14 at the annual meeting of the Ecological Society of America in Sacramento. Scientists say the fish’s Atlantic invasion, believed to have begun in the 1980s, now covers an area larger than the whole United States, decimating native fish in parts of the Caribbean and elsewhere. Most native predatory fish are attracted to prey when their numbers are high—that’s when successful attacks are easy as space for shelter runs out, according to previous research by fish ecologist Michael Webster. As the prey population falls, the native predators often move on to areas where, literally, the fishing is better. This process tends to stabilize prey populations: they shrink when they get too large and grow when they get too small. The new research concludes that lionfish, by comparison, seem to stay in one area even as the numbers of prey drop, and in some cases can eat a population to local extinction. They have unique characteristics that make this possible, and like the terminator, they just will not stop. They “seem to be the ultimate invader,” said Kurt Ingeman, a doctoral candidate in at Oregon State University who presented the findings, building on previous work by his advisor Mark Hixon and fellow graduate students. “Almost every new thing we learn about them is some characteristic that makes them a more formidable predator. And it’s now clear they will hunt successfully even when only a few fish are present. This behavior is unusual and alarming.” Ingeman conducted the research on replicated natural reefs in the Bahamas, measuring the mortality rates of a common lionfish prey, the fairy basslet—a popular aquarium fish. A range of scenarios was set up for examination: reefs with the invasive lionfish, reefs with native predators alone, and various population levels of fairy basslet. Ingeman found that when prey fish were sparse, the mortality with lionfish present was four times higher than that caused by native predators alone. “Reef fish usually hide in rocks and crevices for protection, and with high populations, there is a scramble for shelter,” Ingeman said. “Native predators take advantage of this situation by mostly eating when and where prey are abundant.” In other words, the predators have an easier time when there’s simply not enough shelter to hide their prey. Lionfish, however, have such advantages as an invasive species that they apparently feel no need to move on for better or easier hunting, Ingeman said. Other fish may not recognize them as a predator. Lionfish are also very efficient hunters, are well defended themselves by poisonous spines, can thrive in deep waters, tolerate a wide range of conditions, reproduce quickly most of the year and aren’t picky eaters. Hixon and fellow graduate students have shown that lionfish can wipe out over 90 percent of more of the native fish in some hard-hit areas. Evolutionary pressures may eventually allow native fish to adapt and defend themselves, Ingeman said, but when and how is unclear. “We know that fish can learn and change their behavior, sometimes over just a few generations. But we don’t have any studies yet to demonstrate this is taking place with native fish populations in the Atlantic.”